Field description - Issue key
The issue key is a reference number/string that is unique to each issue in a project.
Project-specific prefixes allow you to tell issues from different projects apart.
Default name: Issue key
Terminology variations: Task key, Case key, Item key, Ticket key, etc. depending on the terminology setting for "Issue".
In-Use: Always. This field is always used and cannot be removed from the issue field configuration.
Mandatory: Yes. This field must be set on an issue.
Data type: Text. Example: "Test-1234". This field is constructed by the issue key number added to the issue key prefix of the project (Defined in the project settings).
Every new issue gets the next higher number. Issue key numbers of deleted issues are not "filled in", the gaps remain in the issue key sequence.
Access restrictions: Always Read-only for all users. No one should be able to edit the issue key.
Relationships/Dependencies: Issue key is not dependent on another field.
Affected by these settings: "Issue key prefix" in Project > Settings > General > Edit project info.
This determines the prefix for the issue key.
Use cases: Issue key is used in all cases, as a reference string.